2.5 V High-Energy Aqueous Lithium-Ion Hybrid Capacitors Using a Sodium Titanate Intercalation Anode and a Pseudocapacitive Manganese Dioxide Cathode.

Abstract

The energy density of aqueous lithium-ion hybrid capacitors (ALIHCs) is generally constrained by the lack of suitable low-potential anodes and the kinetic/capacity mismatch between two electrodes. Here we report a unique high-voltage ALIHC made by pairing a layered sodium titanate intercalation anode with a pseudocapacitive manganese dioxide cathode. The oxygen-deficient titanate nanowire anode features a stable, conductive Ti-O framework with large interlayer spacing, enabling intensive, reversible Li⁺ storage at low potentials (-1.4 to -0.8 V vs saturated calomel electrode) with fast intercalation kinetics. Besides, in situ electrodeposition of manganese dioxide nanosheets onto single-walled carbon nanotubes creates a binder-free cathode with high pseudocapacitance to couple with anode. The resulting ALIHC device achieves an ultrahigh voltage of 2.5 V and delivers remarkable energy and power densities (maximum: 70.74 Wh kg^-1 and 11,500 W kg^-1) even at high total mass loading of 12.1 mg cm^-2, surpassing previously reported ALIHCs and even some typical aqueous Li-ion batteries.